Boiler furnace construction



Aug. 23, 1932. H. P. KIRCHNER BOILER FURNACE CONSTRUCTION I Fild-April .19. 19:50 2 Sheets-Sheet w n I 3'," r," 1 n I Aug. 23, 1932. H. P. KIRCHNER BOILER FURNACE coNsTRUciIoN Filed April 19. 1930 2 Sheets-Sheet 2 VINVENTOR.

Patented Aug. 23, 1932 UNITED: STATES BOBUNDUM COMPANY; SYLVANIA Application filed April 19,

fuel, and particularly powdered coal. The 5 drawings relate to the detailed construction.

of one type of boiler furnace embodying my invention. a H In the utilization of powdered coal there has been a greatlyincreased tendency towards Very rapid rates of combustion. A11

though: there are a number of factors wh ch may determine the limit to which the rate of combustion may be increased, the present practical limit in the case of boiler furnaces is determined by the rate of deterioration of the refractory used as a lining for the combustion chamber.

The breakdown of the furnace lining is due primarily to theaction' of the molten coal ash or slag which accumulates on the walls of the furnace. The principal prob, lem therefore is the regulationof-the wall temperature to such a degree that the slag in contactwith the refractory isno longer sulhciently fluid to have a severe erosive or fluning action on the furnace wall. This regulation is the fcause of considerable. difliculty, and inany expedient's' have been tried in an effort to produce the desiredeflect. Both air and water cooling have been at D i a tempted, but when fireclay refractories are 'used the thermal conductivity of the Wallis so low and the thickness necessary for mechanical strength at high temperatures so great that coohngby this means is inefi'ec tive.

In a copending application of Clarence Hawke, SerialNo. 244,734, filed January 5,

1928, now'United States Patent No. 1,828,-

regulating the Walltemperature'is overcome to agreat extent by the use of an air cooled refractory lining ofsiliconcarbide'. The latter combines strength at: high tempera tures with exceptionally highthermal con ductivity, so that a section may befeniployed which is highly conductive, Thew'alls are cooled by the passage of'airthrough ducts behind the face exposed to the combustion tire clay; I

HENRY P. KIRCHNER OF NIAGARA; ran-Ls,- NEW YORK, AssiGNoR 'r'o. THE can or NIAGARA FALLS, NEW YORK, A 'coRroRA'r oN or 2mm 1 BOILER FURNACE CONSTRUCTION 1930. Serial No. 445,611.

chamber, andthe air thus pre-heated is introdueedinto the furnace and utilized for tivity, the cooling effect can be increased to. as much; as twenty times that obtained with In addition, the amount of cooling 3 been i found to be much more nearly propor--' v tional to the velocity ofthe air circulated through the wall than when fireclay refractoriesare used; and it becomes possible to regulate the temperature oft-he wall within;

certain limitsby avariation in thevelocity 1 65' of the circulating air. As an example,-when the furnace temperature is approximately 130O",(,. the amount of heat extracted 'fIOIIIg a two and one -half inch silicon carbide wall canbe increased from 15000 to 2800013 tiiu per square foot per hour by increasing the velocity of the air from to feet pe r second, a

InIorder to obtain effective regulationct the wall temperature by air cooling, the ther mal conductivity of the refractory lining must be greater than .006 cal/cm /sec,/9C.

refractories varies with the material used as a bond,- but with refractories composed-prim cipally of silicon carbide the conductivity is usually between .02 and .04 cal/crn /s'ec/ c .The thermal conductivity of silicon -carbide and may be slightly higher. t Even when thirty percentclay 1s incorporated into the; 1niX,-a conductivity of .014 ca1/cm /sec,/G,1

may. still be attained. The thermal "conduc:

tivity of self-bonded silicon carbide is ap-' proximately .05 cal/cni /sec../C. "Byfsilicon it carbide i-refractory is .meantfa refractory composed principally of silicon carbide, even, 1"

though it may contain other materialskor bonding agents. 1 y I Y i Y In boiler furnaces operatingat' veryihigh ratingslitis not always possible or practical to cool thewalls to'the desiredtemperaturel,

by air alone; even whensilicon carbide is used. Obviously, if the efiiciency of the fun;

nace is to bespreserved,theheat absorbed by the air in cooling the walls must be re-i ntno-; '1

duced' into 1 the furnace, and a when the; latter 1 is operated at high ratings the'yolume of air necessary for the cooling of all four walls may be so great that its introduction into. the combustion chamber is impractical.

- The alternative'ofusing less air and heating it to a higher temperature is also undesirable, for when this is done the efiiciency of the cooling is greatly decreased; Under these conditions the circulatin air produces much less cooling, not only cause of its higher temperature, but also because oft-he:

limited velocity necessarywhen less air; is used. The latter factor eliminates to a large extent the possibility. of regulating the wall temperature by a variation in the velocity of' the air, which is one of the chiefadvantagesderived from the use of an air-cooled silicon carbidewall structure. In addition, if the same time retains theadvantage of tempera- I tureregulation afforded by-air cooling. In I carrying out this invention,'I employ aboiler air is preheated to extreme temperatures it cannot-be passed through the burner without danger of injuring thesteel and making the fuel sticky. g I "In the present invention I have effected a combination of air-cooled and water-cooled silicon-carbide walls which permits excep-' tionally .high combustion ratings without damage to the refractory lining, and at the furnace in which-one or-more walls are composed ofsilicon. carbide blocks surrounding a water cooling medium which may be directly connected to the boiler'circulating system.- The necessary cooling of the furnace walls in'. excess of that which can be furnished by the amount of airused in combustion is provided by this means. In'the remaining walls a silicon carbide structure is employed wherein cooling is effected by the passage of air through ducts in or behind the wall. The air 'pre-heated by circulation through the wall is introduced into the furnace, and

. flame or the hot products of combustion comthe preheating 'is'suflicient to increase the rate of combustion by affording practically instantaneous combustion of the'particles of fuel. 3

The air circulated through the walls may be introduced directly into the burner or into .thecombustion chamber through suit ably located apertures or ports inthe wall itself. There are certain adv'antagesyh'owever, in the latter procedure. Instead of the ing in direct contact'with the wall, the air issuing into the furnace through the wall affords a protective envelope which produces the sameefi'ect as would additional coolingin the caseof the solid wall. In addition to the cooling effect of this envelope of air, an

oxidizingatmosphere is also provided at the surfaceof the refractory, and the melting point of the slag is thereby considerably raised. The erosive action of the slag 'is principally due to the formationof a lowmelting ferrous silicate, and if conditions are by water,

mined, and regulation cannot readily be effected to correspond with the heat generated in the furnace. If the temperature. gradient in the Wallis such that it will withstand high ratings, the cooling produced atany-rating appreciably below the maximum is so great thatthe air in the vicinity of thewall is chilled to the point where it will not support rapid or instantaneous combustion. j

There is therefore a tendency for a certain proportion of the fuel to pass unburned into the tube passes and thence into the stack.

Although regulation can be obtained with air-cooling alone, the amount of cooling, as previously'pointed out, is so limitedthat protection cannot be economically obtained at high rates of combustion. By embodying one or more water-cooled silicon carbide walls in a furnace employing air-cooling 1n (3011]11I1Ct1011 with a s1l1con carbide refractory,

the hotter air-cooled wall imparts its heat byconvection, conduction and radiation to the water-cooled wall until the tem eratur differences are considerably reduce superfficially, andthe regulation of wall tempera, tureat high ratings 'is just :as effective as when air-cooling alone is used at asome-v what lower rating. Combustion can also bev maintained efliciently at lower ratings than would be possible if air-cooling .werenot used. The factthat pre-heated. air is available to' accelerate and support combustion ofi'ers anvadditional advantage in thatthe,

11 0 loss of unburned fuel which would other-Q wise take place with water-cooled side walls at low rates of combustionis greatly reduced. An example showing a type of. construc' tion which may be employed in carrying out 1 ing drawings. a

Figure 1 represents a vertical 'section through a powdered coal boiler furnace in a plane at right angles to the axis of the boiler itself and parallel to thewater-cooled walls;

Figure 2 shows a section atvright angles to that of Figure 1 along the section I line A.A

,of Figure, 1 parallel to the air-cooled walls 1 2 6- line'3-'-3 o f. Fig.1; and Figure 4 is a frag- Figure 3 is a fragmentary section on the my invention is illustratedin the accompanymentary section on the line 4-4 of Figure 3.

Referringto the drawings in more detail, "2 designates generally a furnace for. heating 8/ b91161 3, the boiler having tubes 4. Two

walls of the furnace and :6' are provided with a lining of a silicon carbide refractory Within which are air-circulating.passagesor ducts 7 and 8, respectively. It will be noted that in the. wall 6 one set of ducts8is located above the other set of ducts 8, the upper and lower ducts being separated by a pa rtition 9. .A blower 1O isprovided for circulating air through theseducts or passages, the air from the blower being delivered to pipes 11 and 12. The pipes 1l,cofnmuni cate with the bottoms of the ducts 8while the pipe 12 discharges air into the top of the ducts 7'. A damper 13 is provided in each of the pipes 11 and 12 for regulatingthe flow of air therethrough.- In this particular type of construction, the air is introduced into the combustion through ports 14 at the ends of the ducts 7, and ports 15 at the ends of the ducts 8, these ports being distributed in such manner as to procure the most effective cooling action of the air circulating through the ducts.

The other two walls 16 are of similar construction, being faced with a silicon carbide refractory and having water-cooled Walls, the water being transmitted through pipes 17 embedded in the walls. These pipes are preferably connected directly to the boiler system by means of headers 18 and 19, and the rate of flow may be controlled by means of suitable valves. Some of the water in the pipes 17 may be vaporized owing to the high thermal conductivity of the silicon carbide walls and the thin layer of refractory 16 shown, for example, in Figure 2.

While the inner face of the walls is comprised of a silicon carbide refractory, the portion of the walls outside the ducts 7 and 8 and outside the pipes 17 is composed of a refractory material having a'comparatively low thermal conductivity, such as fire clay, and which may be covered with suitable insulation, as indicated. 7

A blower 20 is indicated at the right of Figure 1 for discharging powdered coal .through ipes 21 to the outlets or burners 22 at the top of the furnace.

The character of the burner orifice 21 is shown in Figure 3 and in Figure 4. The burner orifice is flattened out and extended in a direction at right angles to the plane of Figure 1 so as to produce a sheet of flame at rightangles to the water-cooled walls and therefore at right angles to the plane of the pipes 17 shown in Figure 1.

In the design of boiler furnaces the burner is often constructed so as to afford a sheet of flame extending over practically the entire width of the furnace, and parallel to one of the furnace walls, or in the case of a square furnace, parallel to two opposite walls. In determining the location of the apertures 14 and 15 for the introduction of air into the furnace, I prefer to introduce the air through the walls which are parallel-to the initial direction of the sheet of flame and in'suchi a manner that the flame is blown "away from the walls. The air is thus introducedat an angle to the sheet of flame rather than in a direction parallel'toit.

1 Other typesof burner than that shfown in the drawings may be used For example,"

one or'more horizontal burners maybe used asan alternative for the type of'burncr shown. In this case'the fuel isjint'roduce d through one or moreport's in theside wall instead of through the top portion of the fur nace." If more'than oneburner is used, it is dcsirable-to 'adjust the burners at such'an' angle with respect to eachother that aswirl ingniotion will be imparted to the flame.

By combining the use of air-cooled silicon carbide Walls with that of water-cooled walls of like material to give additional cooling over the maximum amount obtainable with the volume of air used for combustiomIhave' found that the walls may be protected to a high degreeJeven when very high flame temperatures are reached and that the efficiency of the furnace is not impaired by the cooling so produced.

The amount ofair employed forcombus tion increases as the rate of combustion in creases, since with silicon carbide the coolmg effect is greatly increased by incr'easing the velocity of the circulating'air (which'is notthe case with fire clay and the refractories previously employed), it is thus pos sible within certain limits to maintan a pracl tically constant wall temperature even with increased rates of combustion. The air flow face, as for example twdwalls instead of four, the limits through whichthis regula tron of the wall temperature may be maintamed are greatly increased! Therate of air circulation may be varied by varying the speed of the blower 10 as well ment of the dampers 13. i

In the operationof the furnace the refractory wall is protected by athiniglayerof.

as by adjustsolidified slag. The slag itselfis 'a'poor thermal conductor, and eventwhen a fairly. thin layer has congealed on the furnaee wall,

the temperature gradientmay be so great that. additio'nalslag will no longer solidify but will run down the walls of the fur-" C nace. for the protection of'the refractory lining,

and is one which may bercadilv realized by the wall structure here described. By regulating the velocity of the air or the relative ratio ofthe amountv of air circulating' This represents'an ideal condition" through. the walls compared with that direct ly entering the burner, the wall temperature maybe so regulated that, the layer of solidified, slag is sufficient for protection and yet 1 remains comparatively thin, the remainder of the slag in contact with the wall being sufliciently fluid to permit its ready removal fromthe bottom of the furnace.

In certain types of furnaces the area of v the wall face subjectedtoexcessive temperatures is only a portion of that making up the combustion. chamber. In such a case it is desirable to cool the portion of the wall subiected to extreme conditions to a greater exent than the portions furtherremoved from the fire zone. In order. to secure the advantages of the air-cooled and water-cooled silicon carbide structure described herein, the portion of the furnace subjected to extreme flame temperature may be composed of siliron carbide, one or more walls being air-cooled and the remainder being water-cooled, and the more remote portions of thewall or. combustion chamber made from I rials such as fireclay,

the usual mate I claim as m invention: 1

LA boiler urnace for burning powdered coal fuel athigh rates of combustion and for operating the boiler at correspondingly high ratings comprising in combination a combustion chamber having front, back and side walls with silicon carbide linings for HENRY P. ,KIIROHNER.

theexposed surfaces of said chamber; a burner arranged to project a sheet of flame downward from. an opening in the top of the chamber so that said sheet is initially parallel to the front and back walls, air ducts in one said of said walls for pre-heating air by'transmissionl of heat from theupper por tion :of said sheet of flame, air llllGtS'fOI the air ducts whereby the air thus preheated is admitted to the combustion chamber, another series of air ducts inothe same wall for. preheating air by transmission from the lower portion of the flame and delivering said air at an intermediate level in the combustion chamber, a third series of air ducts arranged in the wall opposite to the burner outlet and arranged to deliver. preheated air to the lowermost portion of the combustion cham ber, boiler tubes extending across the outlet of the combustion chamber above said lastmentioned air-cooled wall, other boiler tubes embedded in the side walls and extending substantially the length thereof, and means for varying the respective rates of air and water cooling.

2. A boiler furnace adapted for burning powdered coal comprising in combination a combustion chamber having front, back and side walls each'consisting of a thick outer wall of poorly conducting refractory and a thin inner lining of highly conducting refractory adjacent the combustion chamber, a burner projecting through the roof of the combustion chamber and having a slit-shaped orifice for the discharge of fuel in a downward direction initially adjacent and parallelto 

